Begin the discussion by showing the class two photographs of the Tacoma-Narrows Bridge, in the state of Washington, in the process of collapsing. You can find these images at the following Web sites:Photo 1Photo 2

2.

Ask students to brainstorm about the causes that forced this bridge to wobble and then fall apart. (You may want to ask them if certain weather conditions may have contributed to the bridge’s collapse.) Write their suggestions on a piece of newsprint. After discussing students’ ideas, explain that the cause of the collapse was winds of more than 40 miles per hour.

3.

Discuss with the class two other bridges that have collapsed:

Silver Bridge, Point Pleasant, West Virginia, 1967. In the worst bridge disaster in the history of the United States, 37 trucks and cars fell into the water when this bridge collapsed. The damage was caused by a broken I-bar, a small metal beam that connects the bridge’s different parts. As engineers found out later, one I-bar had a tiny crack at the time of construction; over time the wear and tear of weather and traffic broke the I-bar apart. Once one side of the bridge fell, the other side couldn’t handle the weight, so it collapsed too.

Melbourne Bridge, Melbourne, Australia, 1968. When constructing the bridge, engineers and architects made a simple mathematical error that resulted in an instability in the bridge’s steel girder box. When some of the steel expanded from heat, the bridge fell 120 feet to the ground.

4.

Using the information about bridge collapses as a starting point for discussion, ask students what variables must be considered when building a bridge. Point out that these include environmental factors, such as wind and temperature, building materials, and shapes used to support the structure. Also, discuss with the class the natural forces with which structures must contend, such as the weight of a building pressing down on the lower columns (compression) and natural stretching of materials (tension). Explain how these factors also must be taken into consideration when designing a bridge.

5.

Divide the class into small groups of three or four students. Tell each group to design a plan, or blueprint, for a bridge to cross a gap in your city or town; the bridge could cross a river or join two sections of land. Their goal is to propose the strongest, safest bridge they can with the least expensive materials. As students work, have them answer the questions listed below and record their findings on the Classroom Activity Sheet: Designing a Bridge.

What natural forces might affect your bridge? How can you compensate for them?

What materials are most suitable for your bridge? Keep in mind wear and tear on the bridge, temperature, wind speed, and expense when making your decision.

How much weight can triangles, rectangles, and arches support? Which is most suitable for your bridge? Why?

To guide students in their research, you may want to distribute copies of the Structures Fact Sheet, which provides information on common forces (such as tension and compression), properties of different materials (such as steel and concrete), and how shapes (such as rectangles and arches) affect designs. To conduct the necessary research, have students visit the Web sites listed below.

Have the groups write down their recommendations and draw their blueprints on the Classroom Activity Sheet: Designing a Bridge. Suggest that each student make a copy of his or her group’s recommendations. Then have the groups present their designs to the class. Give other students a chance to comment on the strengths and weaknesses of each design.

7.

Assign the Take-Home Sheet: Top 10 Construction Achievements of the 20th Century for homework. Students will research one of the structures honored by the architectural community in 1999. They will record important facts about the structure and find out how it is reinforced to protect against destructive forces such as high winds, floods, and earthquakes. After students complete the assignment, have them share their findings with the class.

Students in high school could take this assignment one step further by creating 3-D models of their proposed bridges. Alternatively, they could simulate a famous bridge disaster by first building a small, inexpensive model of a bridge that collapsed, then replicating the forces that caused its collapse. For example, high winds can be simulated using a fan, and an earthquake can be simulated by shaking the table supporting the model. The following Web site on bridge disasters might be helpful in completing this project:http://www.iti.nwu.edu/clear/bridge/bri_dis.html

Which of the following shapes would be best able to handle pressure from the top: horizontal rectangle, arch, or triangle? Why? Which would be the weakest?

4.

If you were developing a list of safety measure for bridges, what items would you include on your list? Why?

5.

In addition to the bridges discussed in this lesson, can you name some other structures, such as dams, tunnels, or buildings, that have collapsed? Why did these structures collapse?

6.

In 1979, the Kemper Arena in Kansas City, Mo., Was hit with severe thunderstorms. Because of its poor drainage systems, the roof filled with water. Why do you think this caused the building to cave in?

Students should be able to work well together, complete the research accurately and thoroughly, develop a reasonable blueprint for a bridge, and clearly present their findings to the class. Use the following three-point rubric to evaluate students’ work during this lesson:

Three points:Students worked well together in their groups, developed an exemplary plan for their bridge, drew an accurate blueprint that was labeled clearly and accurately, and made an interesting presentation to the class.

Two points:Students worked somewhat well together in their groups, developed a reasonable plan for their bridge, drew a somewhat accurate blueprint that was labeled clearly and accurately, and were prepared for their presentation to the class.

One point:Students had some difficulties working together in their groups, developed a partial plan for their bridge, drew a partial blueprint, and made a brief presentation to the class.

To the Rescue!When a structure collapses, federal, state, and local organizations rush to the aid of any victims. Brainstorm with the class which organizations help during a disaster. Ask them about the role of these organizations. Have students each become a “Disaster Action Kid,” visit the Web site for kids set up by the Federal Emergency Management Agency:http://www.fema.gov/kids/

Catastrophe! Great Engineering Failure - and SuccessFred Bortz. W.H. Freeman and Company, 1995.Good engineers should try to anticipate anything that could go wrong with whatever it is they are designing. Most do, and some unfortunately do not. This book examines six cases where a mistake in design led to disaster. The fascinating details of each incident is described, illustrated in photographs and drawings, and analyzed so the reader can understand what went wrong and why.

Collapse: When Buildings Fall DownPhillip Wearne. TV Books, 2000.The author tells the stories of how eleven of the worst structural engineering disasters of the last fifty years occurred. The stories of these disasters are also the stories of the forensic engineers who sifted through layers of debris, studied architectural drawings, and staged reconstructions in order to search for the true cause of each catastrophe.

Definition:A type of bridge made of steel or concrete that is constructed from supporting beams that look like a long box.Context:Box girder bridges, such as the Melbourne Bridge in Australia, are popular because they are light, strong, and economical.

This lesson plan may be used to address the academic standards listed below. These standards are drawn from Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education: 2nd Edition and have been provided courtesy of theMid-continent Research for Education and Learningin Aurora, Colorado.

Grade level:6-8Subject area:TechnologyStandard:Understands the nature and uses of different forms of technology.Benchmarks:Knows that construction design is influenced by factors such as building laws and codes, style, convenience, cost, climate, and function.

Grade level:6-8Subject area:TechnologyStandard:Understands the nature and uses of different forms of technology.Benchmarks:Knows that manufacturing processes use hand tools, human-operated machines, and automated machines to separate, form, combine, and condition natural and synthetic materials; these changes may be either physical or chemical.

Grade level:6-8Subject area:TechnologyStandard:Understands the nature of technological design.Benchmarks:Knows that the design process relies on different strategies (i.e., creative brainstorming to establish many design solutions, evaluating the feasibility of various solutions to choose a design, and troubleshooting the selected design.